Process for the production of a fly ash slurry

ABSTRACT

The present invention describes an improved method for forming fly ash slurry by mixing fly ash and water with an additive containing 0.5-2 wt % ammonium salt of humic acid and 0.03 to 0.05 wt % tannin extract. The product slurry does not require large amount of water for transport to storage space due to its enhanced viscosity and stability.

FIELD OF THE INVENTION

The present invention relates to a process for the production of fly ashslurry.

BACKGROUND OF THE INVENTION

Fly ash is a primary product of coal utilisation and is obtained as afine particulate mineral residue, left behind after all combustibles incoal are burnt out. The current output rate of fly ash from streamraising and other plants utilising pulverised coal is about 10 metrictons per annum. The accumulation without adequate avenues forconsumption or disposal otherwise creates a problem of storage space.Air polluted by boiler chimneys or carried away by prevailing winds fromopen heaps also causes lung disorders such as breathing problems forhuman beings. There is a pressing need felt by planners and operators ofpower stations to discover new areas of usage of fly ash such that thetwin problems of storage and pollution can be mitigated. The absence ofa workable solution has resulted in the stockpiling of fly ash.

Prior art methods for the preparation of an ash suspension comprisesdirecting dry ash from under dust collecting equipment to flushingapparatus of different types or to ejectors, which are supplied withwater at the weight ratio of several times greater that of the ashweight. A large volume of water is required to reduce the surfacetension of ash in order to achieve full moisturisation thereof and, thusa suspension. The suspension of a low concentration is sedimentalbecause it does not have the characteristics of heavy liquid. It issubsequently fed along with a portion of the slag directly to drag pumpswhich force it through to the storage yard by pipelines thehydrotransport apparatus conveying said suspension requires a largevolume of water which is obtained by recycling the water from thestorage yard by return pipelines.

U.S. Pat. No. 4,618,376 discloses a method of continuous production offly ash in water of a suspension a high concentration of ash with thesubsequent addition of slag or granular ash and an installation for theapplication of this method. The production process is divided insubsequent stages and is realised in separate zones of a flow mixer.Ash, slag, water and granular ash are fed in a continuous manner.However, this process suffers from the drawback that the process isdivided into several zones: moisturisation zone, homogenisation zone,and fluidisation zone and the stability of the product is not adequate.

OBJECTS OF THE INVENTION

The main object of the invention is to provide a process for theproduction of fly ash slurry, which overcomes the drawbacks of the priorart enumerated above.

Another object of the invention is to provide a process for theproduction of fly ash slurry with high concentration of fly ash answhich overcomes the problems relating to viscosity, stability andconcentration in the prior art methods.

SUMMARY OF THE INVENTION

Accordingly the present invention provides a process for the productionof fly ash slurry said process comprising mixing fly ash and water withan additive containing 0.5-2 wt % ammonium salt of humic acid and 0.03to 0.05 wt % tannin extract at a temperature in the range of 35 to 50°C. for a time period in the range of 30 to 45 minutes and discharging atambient temperature to obtain the fly ash slurry.

In one embodiment of the invention, the viscosity of the fly ash slurryis in the range of 310 to 340 mPs at 128 sec⁻¹.

In another embodiment of the invention, the process is a one stepprocess.

The invention also relates to a composition for use as an additive inthe production of fly ash comprising 0.5-2 wt % ammonium salt of humicacid and 0.03 to 0.05 wt % tannin extract.

The mixture of the invention is a synergistic admixture with propertiesover and above the aggregate properties of the individual ingredients.

DETAILED DESCRIPTION OF THE INVENTION

The process of the invention involves the addition of a mixture ofammonium salt of humic acid and tannin extract to fly ash and water toform a mixture to obtain a slurry with high concentration of fly ash andwith enhanced stability and viscosity.

Thus the fly ash slurry can easily be pumped in view of the reduction inthe sedimental nature thereof. This reduces the amount of water requiredin prior art processes to pump fly ash to the storage yard.

The process of the invention is explained hereinbelow with reference tothe examples which are illustrative and should not be construed aslimiting the scope of the invention.

EXAMPLE 1

54 g of fly ash, 45 g of water and an additive system consisting of 1 wt% ammonium salt of humic acid and 0.05 wt % of tannin extract aresubjected to mixing in a mixer with an agitating device at a temperatureof 40° C. for 35 minutes. Agitation was maintained at 140 ppm. Theproduct was discharged at ambient temperature. The viscosity of theproduct was found to be 330 mPs at 128 sec⁻¹.

EXAMPLE 2

54 g of fly ash, 45 g of water and an additive system consisting of 1.5wt % ammonium salt of humic acid and 0.05 wt % of tannin extract aresubjected to mixing in a mixer with an agitating device at a temperatureof 45° C. for 35 minutes. Agitation was maintained at 140 rpm. Theproduct was discharged at ambient temperature. The viscosity of theproduct was found to be 338 mPs at 128 sec⁻¹.

EXAMPLE 3

54 g of fly ash, 45 g of water and an additive system consisting of 0.8wt % ammonium salt of humic acid and 0.05 wt % of tannin extract aresubjected to mixing in a mixer with an agitating device at a temperatureof 35° C. for 40 minutes. Agitation was maintained at 140 ppm. Theproduct was discharged at ambient temperature. The viscosity of theproduct was found to be 327 mPs at 128 sec⁻¹.

ADVANTAGES OF THE INVENTION

1. The process is carried out in one step, which overcomes themultiplicity of steps in the prior art processes.

2. The stability of the fly ash slurry obtained is high enabling easypumpability.

We claim:
 1. A process for the production of fly ash slurry said processcomprising mixing fly ash and water with an additive containing 0.5-2 wt% ammonium salt of humic acid and 0.03 to 0.05 wt % tannin extract at atemperature in the range of 35 to 50° C. for a time period in the rangeof 30 to 45 minutes and discharging at ambient temperature to obtain thefly ash slurry.
 2. A process as claimed in claim 1 wherein the viscosityof the fly ash slurry is in the range of 310 to 340 mPs at 128 sec⁻¹. 3.A process as claimed in claim 1 wherein the process is a one stepprocess.